Ultrafine grain fluorescent body

Abstract

An ultrafine grain fluorescent body comprises an ultrafine grain luminescent material containing an activator and having a surface carrying thereon a layer which is formed from a different material from the luminescent material, or which has different properties from those of the luminescent material. The layer forms a heterojunction or p-n junction defining a luminescent mechanism in an interface between the luminescent material and the layer. The heterojunction is formed if the layer is a film of oxide, nitride or any other different substance formed on the surface of the luminescent material, e.g. ZnS, having a grain size of several hundred to several thousand angstroms. Alternatively, the p-n junction is formed if the luminescent material is a p-type (or n-type) semiconductor, and if the layer is a film of an n-type (or p-type) a semiconductor formed on the surface thereof. The fluorescent body of this invention is useful for making an electroluminescent (EL) element having a high luminance, a high luminescent efficiency and a high resolution, and capable of being driven by a low voltage.

What is claimed is: 
     
       1. An electroluminescent element comprising an electroluminescent layer comprising a fluorescent body comprising ultrafine grains of a luminescent material containing an activator and dispersed in an organic binder, said grains having a grain size of several hundred to several thousand angstroms and having a surface layer formed from a different substance than said luminescent material, said surface layer forming a heterojunction defining a luminescent mechanism in an interface between said luminescent material and said surface layer, wherein said surface layer contains the same metallic element as said luminescent material and is a member selected from the group consisting of an oxide, a nitride, a sulfide, and a chloride formed from the metal of said luminescent material by a surface treatment in a gaseous atmosphere. 
     
     
       2. An electroluminescent element as set forth in claim 1, wherein said luminescent material is selected from the group consisting of ZnS, SrS, CaS, Y 2  O 2  S, ZnSiO 4  and ZnO, while said activator is selected from the group consisting of Cu, Cl, I, Al, Mn and Eu. 
     
     
       3. An electroluminescent element as set forth in claim 1, wherein said luminescent material is an n-type semiconductor and said layer is a film of a p-type semiconductor, whereby said p-n junction is formed. 
     
     
       4. An electroluminescent element as set forth in claim 1, wherein said luminescent material is a p-type semiconductor and said layer is a film of an n-type semiconductor, whereby said p-n junction is formed.